Indicator



June 15, 1943. D. w. RANDOLPH 2,321,855

INDICATOR Filed Jan. 17, 1940 3nventors 7/ 47 flow/d iffy/WWW neg Patented June 15, 1943 UNITED STATES PATENT OFFICE INDICATOR Donald W. Randolph, Flint, Mich, assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application January 1'7, 1940, Serial No. 314,205

4 Claims.

tube is supported in a conventional socket II! which is supported in any suitable manner behind the panel.

The indicator tube 5 is of the socalled magic target of an electronic indicator tube to indicate 5 eye or 6E5 type and is a triode amplifier having various measurements. indicating elements associated with the triode Electrical measuring instruments having an elements. As best shown in Figure 3, the indiindicating needle mounted on a moving element eating elements are located in the outer transsupported in bearings are subject to wear when pa e t e d o the tube W h is broken y to subjected to vibration as the element is con- 10 show details thereof. The triode elements which ti uOusly oscillated unless damping means is proare located in the central portion of the tube and vided. The use of an electronic indicator tube are Supported from the p s of the ube n the having a target on which a visible electronic disusual er are not shown in Figure 3. charge is used to give an indication of a variable The indicating elements p i a target it measurable quantity instead of a moving element 0f dished form supported on IOdS e ectrical y ty e instrument; h bee f nd t be t eme1y connected thereto which are also sealed in the well suited for use on vehicles where vibration is p s of the tube, and one of which serves as a present. These tubes, however, require the use target conductor and extends outwardly thereof a constant alug high voltage source of power through. The internal conical surface l9 Of the for their operation which requires a converter for t et is coated w t a material which becomes steppingv up the vehicle battery voltage. visibly fluorescent when bombarded by electrons The present invention therefore has for its oband the outer annular portion 20 adjacent eject a simple, compact and inexpensive indicating to serves as a shield to prevent the electrons from apparatus comprising an electronic indicator reaching the internal surface of the tube. The tube, a power supply therefor operating on a l w target has a central opening 21 through the cenvoltage source and having no wearing parts and ter of which extends the end 23 of the triode a source of variable voltage for controlling the cathode from which electrons are emitted which indication visible on the indicator tube. bombard the target surface IS. A ray control The combined means by which the above and electrode 25 also extends through the opening 2! associated objects are accomplished is described in parallel relationship to the end 23' of the oathas follows and is illustrated in the following ode to control the path of electron flow from the drawings, in which: end 23 of the cathode to the conical surface [9 Figures 1 and 2 are views of a control panel of the target I5. This ray control electrode is having an opening, a calibrated scale adjacent an extension of the triode plate and is electrically thereto, and an electronic indicator tube located connected thereto as will be described later. behind and visible through said opening; When the coated conical surface IQ of the target Figure 3 is a longitudinal sectional view takenv is bombarded by electrons from the cathode it on line 3-3 of Figure 1 with the end portion of becomes visibly fluorescent. The area of the the indicator tube broken away to show details surface bombarded by the electrons is determined thereof and; 4.0 by the voltage impressed on the ray control elec- Figure 4 is a diagrammatic view of the comtrode 25. As the ray control electrode 25 bebined electrical apparatus and the wiring diacomes more positive the greater the area of fiuogram therefor. rescence on the target and at a predetermined As shown in Figures 1 to 3, a sheet metal instruvalue of the entire surface of the target becomes ment panel I is pressed outward at 3 for recep- 4 fluorescent. When the electrode 25 becomes less tion of the outer end of an electronic indicator positive the electron bombardment of the target tube 5. A 90 degree segmental opening 1 is proadjacent this electrode is reduced and a dark vided in the panel I adjacent the end of the tube, portion of segmental form appears on the target. and a scale 8 adjacent the arcuate edge of this This shadow increases angularly and circumferopening allows the extent or area of the electronic entially on either side of the dotted line indidischarging occurring in the end of the tube to cated at A in Figures 1 and 2, which extends be observed and measured. The outer end of the radially outward from the center of the target tube 5 extends through an opening 9 in a sheet and passes through the center of the control elecmetal flange ll fixed to the rear side of the panel trode. The 6E5 tube shown is extremely sensil, for support therein, and the base I2 of the tive to changes in voltage of the ray control electrode 25 in the range from zero dark area to approximately 100 degrees of dark area but other tubes are available which give a greater angular spread. The 90 degree segmental opening 1 allows one fourth of the area of the target to be observed and one radial edge of this opening coincides with line A so that one edge of the dark area adjacent the fluorescent areas serves as the indicator of variation of the shadow area and the fluorescent area, which may be measured on the scale 8. A cap or shield 21 is located adjacent the ends of the cathode and the ray control electrode to prevent the electrons from reaching the inner end surface of the tube. The cap is held in the center of the tube by rods 29, one of which is shown in Figure 3. These rods are welded to the cap and target at points 90 degrees from where the ray control electrode passes through the opening 2| in the target.

The tube elements, power supply means and control means for the tube are shown in diagrammatic form in Figure 4. The triode elements as well as the indicating elements of the tube are shown'diagrammatically in this figure and the circuit connections from these elements to the power supply means are also shown. The triode, heater or filament is indicated at 3|, the cathode at 33, the plate at 35 and the grid at 31. The heater 3| is connected across a battery 39 which may be an ordinary 6-volt storage battery and the heater cathode 33 is connected to the positive terminal of this battery. The grid 31 is connected to a source of variable voltage and controls the voltage of the ray control electrode 25 and the fluorescent area variable on the target l5. The characteristics of the tube are such that the visible fluorescent area is proportional to the grid voltage. This variable voltage source may be supplied by any well known means, for example, by a generator, the terminal voltage of which is directly proportional to speed so that the tube will indicate speed. The means shown for varying the voltage is a potentiometer indicated .at '41. This potentiometer comprises a resistance element 43 connected across the battery 39 so that a constant value of current flows therethrough, and a movable contact 44 is in electrical contact with the resistance and movable with respect thereto. The contact 44 is connected to the grid 31, and the voltage impressed thereon is proportional to the position the contact occupies on the resistance element. The grid, therefore, by this means can bemade more or less positive by moving the contact along the resistance element to make the plate 35 and the ray control electrode 25 more or less positive with respect to the target [5, to control electron flow between the end 23 of the cathode to the target l so that the fluorescent area visible therein is proportional to the movement of the contact 44. The ray control element 25 is an extension of the plate 35, as best shown in Figure 4.

Any means, such as a temperature, pressure, or speed responsive'device having an element movable in proportion to variations in any of these quantities may 'be operatively connected to the movable contact 44 to move it so that the variation in fluorescent area visible in the tube will indicate variations in any of these quantities. The scale 8 adjacent the end of the tube may be calibrated, therefore, to indicate tem perature in degrees as shown in Figure 2 or pressure in-pounds per square inch as shown in Fig ure 1 or in any other units desired.

The high voltage plate and target supply necessary for producing the electronic discharge in one or more indicator tubes is furnished by an interrupter 45, a transformer 4'! and a triode rectifier 49. The interrupter comprises a glass tube 5| substantially filled with mercury and having two electrodes 53 and 55 extending into the tube and sealed in the walls thereof. The inner end of the electrode 53 is embedded in a tip 51 of high resistance material and is supported i an inwardly projecting tubular portion 59 of tube having a small opening 6| in the end thereof so that only a small area of the tip 51 is in contact with the mercury. The inner end of the other electrode 55 is positioned so that it is maintained in contact with the mercury at all times. The outer ends of the electrodes 53 and 55 are connected in series with the primary winding 63 of the transformer 47 and the battery 39, and the current flowing in this circuit cause the tip 51 to be heated sufiiciently to vaporize the mercury in contact with the tip causing interruption of the current flow, which then allows the mercury to condense so that the circuit is again completed. This cycle of operation occurs at regular intervals, depending upon the physical dimensions of the parts of the interrupter. The constant frequency of current interruption in the primary coil induces a high voltage alternating current in the secondary coil 65 of the transformer, the center tap 61 of which is connected to the positive terminal of the battery and end taps of which are connected to electrodes 69 and H of the triode rectifier 49. The rectifier is of the full wave type and the positive or output electrode '13 is connected to the target l5 which is also connected to plate 35 through a resistor 15. The target and plate are thus maintained at a higher voltage than the battery and at substantially constant potential as the constant frequency interruptions of current in the primary coil of the transformer caused by the automatic mercury interrupter produce a constant frequency of flux interlinkages between the primary and secondary coils of the transformer and therefore a constant value of alternating current of high potential is impressed on the rectifier which rectifies the alternating current and is connected to the target and plate of the tube.

The operation of the indicator apparatus is as follows:

When the movable contact 44 of the potentiometer 4| is moved in either direction to make the triode grid 31 more or less positive, the triode plate 35 and ray control electrode 25 become more or less positive with respect to the target l5. When the potential of the plate and ray control electrode is substantially the same as that of the target [5, the entire conical surface I9 of the target becomes fluorescent and the radial edges of this fluorescent area meet on the line A shown in Figures 1 and 2. There is no current flowing in the triode plate circuit when this condition is reached and therefore no potential drop occurs across the resistor 15. When the contact 44 is moved to a different position the plate 35 and ray control electrode are made less positive with respect to the target l5 and current will flow in the plate circuit and a potential drop will occur across the resistor 15. The potential of the plate and ray control electrode under these conditions approaches the potential of the cathode 33 and a shadow or dark area of segmental form will appear on the target adjacent the ray control electrode. Each edge of the shadow will move angularly an equal amount away from the line A proportional to the voltage impressed on the grid, which is proportional to the distance the resistance contact 46 is moved by the particular measuring device which is operatively connected thereto. As only one edge of the shadow is visible through the opening 1 in the panel I, this edge acts as a pointer and the scale 8 adjacent this opening may be divided and numbered corresponding to the units measured.

It will be evident that any number of indicator tubes may be mounted on an instrument panel to indicate various measurements. Each of these tubes may be connected to the battery and high voltage supply in the manner shown and described, the indication of each tube being controlled by the amount of voltage impressed on the grid 3'! controlled by any measuring device. The measuring device may be located at any distance from the instrument panel or power source. The accuracy of the measurements visually observed, on the tube target is due to the constant potential supplied to the tube for producing the electronic discharge; the variable voltage supplied to the grid causes a variation in the path of the electronic discharge to vary the visible fluorescent area proportional to the change in the grid voltage.

I claim:

1. An indicator comprising an electronic discharge tube having a target, said target having an annular surface coated with a fluorescent material, a cathode located centrally With respect to said annular target surface for causing an electron flow to said target coating to render it visibly fluorescent, an electrode radially spaced between said cathode and said annular target surface for controlling the path of electron flow between the cathode and target to vary the visible fluorescent area of the target coating and a scale of arcuate form located adjacent the annular target surface, said scale having a radial edge in alignment with said cathode and said electrode to measure the change in visible fluorescent area on the target coating.

2. An indicator comprising an electronic discharge tube having a target, said target having an annular surface coated with a fluorescent material, a cathode element located centrally with respect to the annular target surface to cause an electronic bombardment of the annular target surface to render it visibly fluorescent, a control electrode radially spaced between said cathode and said annular target surface to vary the path of electron flow to the target coating thereby to cause a variation in the visible fluorescent area thereon and a panel having a sector shaped opening through which only a sector shaped area of said annular target may be viewed and a scale adjacent the arcuate portion of the opening for measuring the angular variation in visible fluorescent area on said target.

3. An indicator comprising a multi-element electronic discharge tube having a target, said target having a dished annular surface coated with a fluorescent material, a cathode fixed centrally with respect to said annular target surface for causing an electronic bombardment thereof to render it visibly fluorescent, a control electrode radially spaced between said cathode and said dished annular target surface to vary the path of electron flow to the coating of said target and thereby vary the visible fluorescent area on said annular target surface, an opaque panel having a sector shaped opening and a scale on said panel adjacent the arcuate portion of the opening and means supporting said tube behind said panel opening with the arcuate portion of said opening located in concentric relation with said annular target surface and with one of the radii of the sector shaped opening located in radial alignment with both said cathode and said control electrode whereby variation in the fluorescent area on that portion of said annular target visible through the sector shaped opening may be accurately measured on said scale.

4. An indicator comprising a multi-element electronic discharge tube comprising a target coated with fluorescent material, a cathode adjacent the target, a control grid between the target and cathode, a panel covering a portion of said target, the edge of said panel being in alignment with said cathode and control grid, and a calibrated scale adjacent said target and the edge of said panel to measure the change in visible fluorescent area on the target coating.

DONALD W. RANDOLPH. 

